The main A489 road between Newtown and Kerry will be closed for two weeks from Monday.
The closure is to allow contractors on the Newtown bypass to undertake work around the Lower Brimmon area.
Diversions will be in place, although some residents fear local lanes will become congested with motorists using them instead of the official diversion route.
Contractors, Alun Griffiths, have said they will be working extended hours and weekends and are “confident that the measures will ensure that the works will be completed within the two week closure.”
Cabinet Member for Highways, Councillor Liam Fitzpatrick said: “The alignment work is complex and requires significant traffic management to make sure motorists and bypass construction workers are safe throughout the operation.
“A number of management operations were considered and the two week closure with a diversion, although frustrating and inconvenient, is judged to cause the least disruption.
“An infrastructure project the size of Newtown bypass was always likely to have an impact on the road network and we ask motorists for their patience. The alternative to the road closure would have been traffic lights for 12-weeks and a HGV ban.
